Studies on semduramicin and nutritional responses. 1. Level and source of protein

An experiment was conducted to determine whether feeding semduramicin at re commended levels (25 mg/kg) would affect the broiler chicken's response to dietary protein; and to determine whether protein source (all vegetable, co rn and soybean meal, vs 12% high animal protein ingredients) would affect t he response to semduramicin. Semduramicin was fed to half of 1,584 male Ros s x Ross broilers in floor pens during the growing phase (18 to 35 d). Thre e protein fortification levels were also fed with protein and amino acid mi nimum restrictions at 80, 100, and 120% of NRC (1994) recommendations. At 3 5 d, semduramicin was found to cause a slight growth depression in body wei ght gain only when low protein levels were fed (P = 0.051). After a 7-d wit hdrawal period, compensatory gains occurred (P = 0.006) such that there was no interaction effect of semduramicin by protein level for 42-d body weigh t (P = 0.75). Birds fed the diets containing high animal protein were sligh tly heavier than those fed control diets containing all-vegetable protein ( 2.40 +/- 0.02 vs 2.36 +/-0.01 kg/bird; P = 0.059). Semduramicin feeding did not affect feed consumption (2.43 +/- 0.03 vs 2.40 +/- 0.02 kg per bird du ring the growing period when it was fed) so that overall feed conversion ra tios were identical to two decimal places (1.90 +/- 0.02 vs 1.90 +/- 0.02). Neither did semduramicin affect feathering score or weight of the No. 8 pr imary feather, except that feather weight tended to be improved by semduram icin feeding with the diets containing ingredients high in animal protein ( P = 0.067).